Spectroscopic analysis of alkenes:

 The IR spectrum of an alkene depicts a characteristic stretching absorption for the C=C bond at 1680-1620 cm^-1. This is little higher as compared to the corresponding absorptions for aromatic rings. Though, conjugation along with aromatic rings, carbonyl groups or other double bonds can lower the absorption frequency as far as 1590 cm^-1. A number of carbonyl absorptions can take place in similar region but are usually stronger if they are present.

The C-H stretching absorption of an alkene proton takes place in the region 3095-3010 cm^-1 but is usually weak and could be hard to spot. It can as well be confused with the C-H stretching absorptions for an aromatic ring. Alkene C-H out of plane bending absorptions may occasionally be visible in the fingerprint region and can point out the substitution pattern. For instance, an absorption in the region 730-675 cm^-1 is indicative of cis alkenes, whereas an absorption in the region 990-960 cm^-1 is indicative of Trans alkenes. Monosubstituted alkenes encompass two absorptions at 910 and 990 cm^-1.

For the protons and carbons the nmr signals of an alkene group appear at characteristic positions in their respective spectra (usually 4.5-6.5 ppm for ¹H spectra and 80-145 ppm for ¹³C spectra). The chemical shifts of every signal can point out the stereochemistry of the alkene, and nmr tables are obtainable to work out the theoretical shifts relies upon the substituents present and their relative positions. If coupling is observed among the alkene protons in the proton spectrum, the coupling pattern and the coupling constants can point out the stereochemistry. For instance, the coupling constants for protons that are trans or cis with respect to each other are generally 14-16 Hz and 6-8 Hz correspondingly. The coupling constants for geminal protons (that is protons on similar alkene carbon) are small (generally 1-2 Hz).

In the ethane's uv spectrum, the λ_max for the π-π* transition is 171 nm. For conjugated systems the wavelength of this type of transition increases and can point out the amount of conjugation also the substitution pattern.